San Francisco has issued building permits for both phases of Mission Bay Block 4 East, clearing the way for two affordable-housing towers rising 16 and 23 stories along 3rd Street. The project is slated to bring 398 apartments and more than half a million square feet of space to a one-acre site between Mission Rock Street and China Basin Street, with construction estimated to run just over $125 million.
The permits cover both development phases, according to San Francisco YIMBY, which reported the property sits across from the Third Street light rail and the Mission Rock master plan site. Phase one is a 16-story tower at 506 China Basin Street with 165 apartments, while phase two is planned to rise an estimated 242 feet at 505 Mission Rock Street with 233 apartments. The unit mix across both buildings calls for 105 one-bedrooms, 190 two-bedrooms, 96 three-bedrooms, and seven four-bedroom homes.
Notably, the apartment count has shifted slightly between project updates. The outlet's October report lists 398 apartments, while an earlier description from June 2025 put the figure at 400 apartments, both tied to the same half-million-square-foot build-out. Parking figures have also moved: the current report lists space for 88 cars and 256 bicycles, up from an earlier tally of 78 cars and the same 256 bicycle spaces.
Who's Building It, and Where the Money Comes From
Curtis Development and Bayview Senior Services are the joint developers behind the project, with Perry Architects and Y.A. Studio jointly handling design work meant to complement neighboring buildings in Mission Rock and the Luma Hotel. Swinerton and Rubecon are set to form a joint venture to serve as general contractor, per the same report. The Office of Community Investment and Infrastructure is listed as the property owner.
Income eligibility for the future residents has also been described two different ways across project materials. The project's own website states homes will be available to families earning 35% to approximately 95% of area median income, while the June 2025 project description put that range at 30% to 95% of area median income.
No Firm Finish Date, but a Construction Roadmap Exists
The October permit report states that a completion timeline for the project has not yet been shared. Separately, the project website, mb4e.com, lays out a tentative schedule: phase one, with its 165 apartments, is planned to begin construction in early 2027 and start leasing in 2029, while phase two's roughly 233 apartments are projected to break ground in 2028 and begin leasing in 2030. Those dates are described as subject to financing availability.
The project fits into a much larger pattern of redevelopment across Mission Bay South, a 238-acre mixed-income, transit-oriented district whose North and South Redevelopment Plans were approved by the city in November 1998, according to the Office of Community Investment and Infrastructure. That same agency describes the Third Street light rail running through the district as a local transit line connecting southeastern San Francisco neighborhoods to downtown and Chinatown. Separately, a 2026 accomplishments report from onesanfrancisco.org notes that OCII began predevelopment on 396 affordable units in Mission Bay, including 233 units that represent the agency's first under SB 593 Replacement Housing legislation.
A Neighborhood Already Reshaping Its Skyline
Block 4 East isn't rising in isolation. Just across the way, the Mission Rock development has already delivered its first residential building, The Canyon, a 23-story, 283-unit mixed-use tower that includes 102 affordable units, 58,000 square feet of office space, and ground-floor retail, according to Multi-Housing News. At full build-out, Mission Rock is expected to include 1,200 residential units, with 40% designated affordable, alongside 1.4 million square feet of office and lab space and eight acres of public parks.
Mission Rock is a joint venture between Tishman Speyer and the San Francisco Giants; the Port of San Francisco serves as public landowner and development partner. It is built on Seawall Lot 337 and Pier 48 across McCovey Cove from Oracle Park, per SF Planning. Its first two residential buildings, Verde and The Canyon, are both now leasing, and the development includes China Basin Park, a five-acre stretch of lawns, plazas, and waterfront space, according to missionrock.com. Together with Block 4 East, the two projects point to a stretch of the city's southeastern waterfront still very much under construction, with thousands of new homes — a meaningful share of them affordable — still working their way through permitting and financing before anyone moves in.
